The present invention relates to a fuel-air mixture-forming device for internal combustion engines, the device having a nozzle body of rotational symmetry which, together with a throttle member or rotational symmetry which is displaceable in it, forms a convergent-divergent nozzle which discharges into a radial diffusor, there being a slot which extends around the nozzle in the vicinity of its narrowest cross section, and discharges into the diffusor. At least one fuel line opens into the slot.
The more homogeneous the fuel-air mixture has been made by the mixture-forming device before entering the combustion chambers of the engine and the smaller the droplets of fuel present in this mixture, the smaller the actual fuel consumption will be and the more uniform the combustion, not only upon successive work cycles in one and the same cylinder but also in all cylinders of the engine, and the higher the obtainable engine output will be.
In a mixture-forming device of the type indicated known from West German 36 43 882 A1, the fuel is fed in the form of a film over the entire circumference of the nozzle in a direction transverse to the direction of flow of the air flowing through the nozzle. The main mass of the fuel fed is subsequently atomized by the mass of air flowing transverse to the film of fuel, the size of the resultant droplets decreasing with increasing speed of the stream of air. As a result of adhesion, the fuel flowing in the radial slot adheres to its walls and even after passage into the divergent nozzle region of the nozzle body, the fuel continues to adhere to the walls thereof in a more or less thick film.
The nozzle discharges into a strongly outwardly curved radial diffusor, with the result that the film of fuel detaches itself in the form of larger droplets in the region of the curvature due to the merely low speed of the air and the centrifugal action there, in contrast to the much smaller droplets in the center of the flow of the fuel-air mixture. The result is a thicker film of fuel in the intake pipe with the resultant disadvantage of a non-uniform composition of the mixture composition for the individual cylinders and for one and the same cylinder upon successive operating cycles, which leads to a non-steady loading of the engine and causes changes in the average composition of the exhaust, so that an impairment of the exhaust gas quality can be noted even behind the catalyst.